package cn.net.dpi.util;

import org.springframework.stereotype.Component;

/**
 * Copyright(c) 2021 Dayou Positioning Intelligence Co.,Ltd
 * All rights reserved.
 *
 * @Description
 * @Date 2021/9/16
 * @Author changguoshan (changguoshan@dayoupi.cn)
 * @Version 0.1
 * @Reviewer
 */
@Component
public class SnowFlakeUtil {
    /**
     * 起始的时间戳
     */
    private final static long START_STAMP = 1480166465631L;

    /**
     * 每一部分占用的位数
     */
    private final static long SEQUENCE_BIT = 12; //序列号占用的位数
    private final static long MACHINE_BIT = 5;  //机器标识占用的位数
    private final static long DATACENTER_BIT = 5;//数据中心占用的位数

    /**
     * 每一部分的最大值
     */
    private final static long MAX_DATACENTER_NUM = ~(-1L << DATACENTER_BIT);
    private final static long MAX_MACHINE_NUM = ~(-1L << MACHINE_BIT);
    private final static long MAX_SEQUENCE = ~(-1L << SEQUENCE_BIT);

    /**
     * 每一部分向左的位移
     */
    private final static long MACHINE_LEFT = SEQUENCE_BIT;
    private final static long DATACENTER_LEFT = SEQUENCE_BIT + MACHINE_BIT;
    private final static long TIMESTAMP_LEFT = DATACENTER_LEFT + DATACENTER_BIT;

    private long datacenterId=1;  //数据中心
    private long machineId=2;    //机器标识
    private long sequence = 0L; //序列号
    private long lastStamp = -1L;//上一次时间戳

    public SnowFlakeUtil() {
    }

    public  SnowFlakeUtil(long datacenterId, long machineId) {
        if (datacenterId > MAX_DATACENTER_NUM || datacenterId < 0) {
            throw new IllegalArgumentException("datacenterId can't be greater than MAX_DATACENTER_NUM or less than 0");
        }
        if (machineId > MAX_MACHINE_NUM || machineId < 0) {
            throw new IllegalArgumentException("machineId can't be greater than MAX_MACHINE_NUM or less than 0");
        }
        this.datacenterId = datacenterId;
        this.machineId = machineId;
    }

    /**
     * 产生下一个ID
     * @return
     */
    public synchronized String nextId() {
        long currStmp = getNewest();
        if (currStmp < lastStamp) {
            throw new RuntimeException("Clock moved backwards.  Refusing to generate id");
        }

        if (currStmp == lastStamp) {
            //相同毫秒内，序列号自增
            sequence = (sequence + 1) & MAX_SEQUENCE;
            //同一毫秒的序列数已经达到最大
            if (sequence == 0L) {
                currStmp = getNextMill();
            }
        } else {
            //不同毫秒内，序列号置为0
            sequence = 0L;
        }
        lastStamp = currStmp;
        return Long.toString ((currStmp - START_STAMP) << TIMESTAMP_LEFT //时间戳部分
                | datacenterId << DATACENTER_LEFT      //数据中心部分
                | machineId << MACHINE_LEFT            //机器标识部分
                | sequence);                            //序列号部分
    }

    /**
    　　* @description: 获取下一个时间戳
    　　* @return 时间戳
    　　* @throws
    　　* @date 2021/9/16
    　　*/
    private long getNextMill() {
        long mill = getNewest();
        while (mill <= lastStamp) {
            mill = getNewest();
        }
        return mill;
    }

    /**
    　　* @description: 获取当前时间戳
    　　* @return 当前时间戳
    　　* @throws
    　　* @date 2021/9/16
    　　*/
    private long getNewest() {
        return System.currentTimeMillis();
    }
}
